Solar cells generate electricity using the photovoltaic effect of a p-n junction which converts photons of sunlight into electricity. In the solar cell, front and rear electrodes are formed on upper and lower surfaces of a semiconductor wafer or substrate with the p-n junctions, respectively. Then, the photovoltaic effect at the p-n junction is induced by sunlight entering the semiconductor wafer and electrons generated by the photovoltaic effect at the p-n junction provide electric current to the outside through the electrodes. The electrodes of the solar cell are formed on the wafer by applying, patterning, and baking an electrode composition.
Parameters determining solar cell efficiency include open circuit voltage (Voc), short circuit current density (Jsc), and fill factor (F.F.). The open circuit voltage (Voc) is a potential difference between opposite ends of a solar cell when the solar cell is irradiated with light in an open circuit state, i.e. with infinite impedance applied thereto. For example, in a homo-junction solar cell, a maximum possible open circuit voltage is given by a difference in work function between a p-type semiconductor and an n-type semiconductor. Since the work function is determined by the band-gap of a semiconductor, use of a material having a high band-gap provides substantially high open circuit voltage. The short circuit current density (Jsc) is a reverse (negative) current density when the solar cell is irradiated with light in a short circuit state, i.e. without any external resistance. The short circuit current density preferentially depends upon the intensity and spectral distribution of incident light. However, under these conditions, the short circuit current density depends upon how effectively electrons and holes excited by light absorption are sent from the solar cell to an external circuit without recombining with each other and lost thereof. Here, loss of electrons and holes due to recombination occurs inside and/or at an interface between materials in the solar cell.
Therefore, there is a need for a composition for solar cell electrodes that can secure excellent open circuit voltage and short circuit current density so as to improve conversion efficiency of solar cells.